Holographic Reticle and Patterning Method

ABSTRACT

A hologram reticle and method of patterning a target. A layout pattern for an image to be transferred to a target is converted into a holographic representation of the image. A hologram reticle is manufactured that includes the holographic representation. The hologram reticle is then used to pattern the target. Three-dimensional patterns may be formed in a photoresist layer of the target in a single patterning step. These three-dimensional patterns may be filled to form three-dimensional structures. The holographic representation of the image may also be transferred to a top photoresist layer of a top surface imaging (TSI) semiconductor device, either directly or using the hologram reticle. The top photoresist layer may then be used to pattern an underlying photoresist layer with the image. The lower photoresist layer is used to pattern a material layer of the device.

This application is a divisional of patent application Ser. No.10/792,084, entitled “Holographic Reticle and Patterning Method,” filedon Mar. 3, 2004, which application is incorporated herein by reference.

REFERENCE TO COMPUTER PROGRAM LISTING APPENDIX

The material on two identical compact disks, Copy 1 and Copy 2, isincorporated herein by reference. Each compact disc contains a fileentitled “TSM02-0658, Appendix A”, created on Sep. 18, 2003, having asize of 9 KB.

TECHNICAL FIELD

The present invention relates generally to lithography for semiconductordevices, and more particularly to a reticle design including aholographic pattern and methods of patterning a semiconductor waferusing a holographic reticle.

BACKGROUND

In semiconductor device manufacturing, features and geometric patternsare created on various layers of semiconductor wafers using opticalphotolithography. Typically, optical photolithography involvesprojecting or transmitting energy or light through a mask or reticlehaving a pattern made of optically opaque areas and optically clearareas. Alternatively, a mask or reticle may be reflective rather thantransmissive. A phase-shifting mask (PSM) is a type of mask or reticlethat uses a phase difference rather than a transmittance difference togenerate patterns.

A mask is generally used to pattern an entire wafer at a time, while areticle is used to pattern a portion of a wafer, e.g., instep-and-repeat projection systems. The term “reticle” as used hereinrefers to any patterning device having a pattern thereon that may betransferred to the entire surface of a semiconductor wafer, or a portionof a surface of a semiconductor wafer or target.

A prior art reticle 10 used to pattern a target such as a semiconductorwafer is shown in FIG. 1. The reticle 10 may comprise a binarychrome-on-glass mask, for example. A transparent substrate 12 comprisingsilicon quartz, for example, is provided. An opaque layer 14 isdeposited over the substrate 12. The opaque layer 14 typically compriseschrome, for example. The opaque layer 14 is patterned with a desiredpattern so that light may pass through transparent regions 16 of theopaque layer 14. The opaque layer 14 of the reticle 10 may be patternedby depositing a photoresist, and patterning the photoresist directlyusing an electron beam or laser to expose the resist, as examples. Thephotoresist pattern is then transferred into the opaque layer, e.g., bywet etching.

The reticle 10 may be used to pattern a photoresist layer on a targetsuch as a semiconductor wafer 20, shown in FIGS. 2 and 3. FIG. 2 shows atop view of the wafer 20 and FIG. 3 shows a cross-sectional view of thewafer 20 at 3-3′ of FIG. 2. The wafer 20 may comprise a substrate orworkpiece 21 having a material layer 23 disposed on the top surface thatwill be patterned. A photoresist layer 22 is deposited on the topsurface of the wafer 20 over the material layer 23 to be patterned. Thephotoresist layer 22 is patterned by illuminating the photoresist layer22 of the wafer 20 with energy, e.g., light, through the reticle 10 ofFIG. 1. The photoresist layer 22 is then developed, and portions ofphotoresist layer 22 are removed, leaving a pattern in the photoresistlayer 22 that corresponds with the pattern on the reticle 10, shown inFIG. 1. The optically opaque areas 14 of the reticle 10 block the light,thereby casting shadows and creating dark areas, while the opticallyclear areas 16 allow the light to pass, thereby creating light areas onthe wafer 20. The light areas and dark areas may be projected onto andthrough an optional lens (not shown), and subsequently onto thephotoresist layer 22 of the wafer 20.

When the wafer photoresist layer 22 is developed, exposed areas of thephotoresist may be removed, leaving a positive image of the reticle 10in the photoresist layer 22, e.g., for a positive photoresist.Alternatively, unexposed areas of the wafer photoresist layer 22 may beremoved, leaving a negative image of the reticle in the photoresist,e.g., for a negative photoresist (not shown).

The patterned photoresist 22 is then used as a mask to pattern theunderlying material layer 23 of the wafer 20. For example, thephotoresist 22 may be left in place on the wafer 20 while the wafer 20is exposed to a dry or wet etchant to remove exposed portions of thematerial layer 23. The photoresist 22 is removed either in a separateetch step, or at the same time the material layer 23 is etched. Thepatterned material layer 23 is left remaining over the workpiece 21 topsurface. Semiconductor wafers 20 are typically manufactured by thedeposition and patterning of multiple layers of insulating, conductiveand semiconductive materials, in the manner described above. Another wayto form the desired layout on the wafers 20 is to process thelithography and developing process, and then deposit a metal or othermaterial layer over the patterned material layer 23, using a damasceneprocess.

The original image of prior art reticles 10 is typically duplicated onthe wafer 20, either in the pattern original size, in a 1× magnificationscheme, or alternatively, a 4-5× magnification reduction may be used forprojection lithography systems to produce a wafer having a materiallayer 23 pattern that is ¼ or ⅕ smaller than the reticle 10 pattern, forexample. Thus, a one-to-one corresponding relationship exists in priorart reticle 10 patterns and images produced on the wafer 20.

A disadvantage of prior art lithography is that this one-to-onerelationship between the reticle 10 and the wafer 20 can result in areticle defect 18, particularly if the defect is large, inducing a flaw23 a on a wafer 20. Hard defects and/or soft defects can be formedduring the manufacturing process or handling of a reticle 10. Softdefects refer to pattern defects that may be removed by cleaning,whereas hard defects generally refer to pattern defects that cannot beremoved by a cleaning process. Reticles 10 having relatively largereticle defects 18 are unacceptable because the defect may betransferred to the target 20.

Because reticles 10 are typically expensive and time-consuming tomanufacture, attempts are usually made to repair them, rather thanscrapping them. Larger hard opaque defects 18 are often removed using alaser to evaporate unwanted material. However, reticle 10 defectinspection and repair are difficult, time-consuming tasks. Also, laserrepair of a reticle 10 can damage the reticle substrate, leaving a laserburn and possibly creating a printable defect on the substrate 21. Therepair of some reticle 10 defects is often impossible to achieve.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention, in which a layout pattern or image to betransferred to a target is converted into a holographic representationof the image, and a hologram reticle is manufactured that includes theholographic representation. The hologram reticle is then used to patterna wafer. Advantageously, imperfections or defects on the hologramreticle are not transferred to the wafer. The original image ispartitioned and encoded across the entire hologram reticle, which breaksthe one-to-one corresponding relationship between defects on the reticleto the wafer. A defect on the hologram reticle does not directly inducea flaw on a wafer, but rather, the defect influence is spread into theentire hologram reticle image, and merely affects the intensity orcontrast of the hologram reticle slightly.

In accordance with a preferred embodiment of the present invention, alithography reticle includes a material having a pattern, the patternincluding opaque regions and transparent regions, the pattern comprisinga holographic representation of an image, wherein the holographicrepresentation of the image is formed using a Computer-GeneratedHolography encoding technique.

In accordance with another preferred embodiment of the presentinvention, a method of manufacturing a lithography reticle includesproviding an image, creating a holographic representation of the imageusing a local encoding technique (LET), providing a material, andpatterning the material with the holographic representation of theimage, wherein the patterned material comprises transparent regions andopaque regions.

In yet another preferred embodiment of the invention, a method ofpatterning a target includes providing a target, the target having a topsurface, the target top surface having a material layer disposedthereon, a first photoresist layer disposed over the material layer, atransparent spacer material disposed over the first photoresist layer,and a second photoresist layer disposed over the spacer material. Themethod includes patterning the second photoresist layer of the targetwith a holographic fringe representation of an image.

Another embodiment of the invention is a method of patterning a target.The method includes providing a target, the target having a top surface,the target top surface having a photoresist layer disposed thereon, andproviding a lithography reticle, the lithography reticle comprising aholographic representation of an image to be patterned on the target.The photoresist layer is patterned with a three-dimensional patternusing the lithography reticle, and depositing a material layer over thephotoresist layer. The photoresist layer is removed, leavingthree-dimensional structures comprised of the material layer disposedover the target.

An advantage of preferred embodiments of the present invention includesproviding a defect-withstanding reticle for patterning a target. Defectson the hologram reticle do not result in the formation of defects on thepatterned target surface. Thus, there is a reduced need for repair ofdefects on the reticle, resulting in a cost savings. The depth of focus(DOF) may be increased to extend the lithography process window,particularly on a topographic substrate. A further advantage ofpreferred embodiments of the present invention is the ability toprecisely control and decrease the DOF, and form three-dimensional (3-D)structures in the photoresist layer on the target.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a top view of a prior art reticle having a defect thereon;

FIG. 2 shows a top view of a prior art wafer upon which the reticledefect has been transferred;

FIG. 3 shows a cross-sectional view of the wafer shown in FIG. 2;

FIG. 4 is a flow chart showing a method of manufacturing and using ahologram reticle in accordance with embodiments of the presentinvention;

FIG. 5 shows a top view of a hologram reticle having a holographicfringe pattern in accordance with an embodiment of the presentinvention;

FIG. 6 illustrates a cross-sectional view of the hologram reticle shownin FIG. 5, including a substrate and an opaque material patterned with aholographic representation of an image to be transferred to a targetdisposed over the substrate;

FIG. 7 illustrates an alternative embodiment of a hologram reticleincluding a phase-shifting material formed over portions of theholographic fringe pattern;

FIG. 8 shows a side view of the hologram reticle shown in FIG. 5;

FIG. 9 illustrates a top view of a hologram reticle in accordance withan embodiment of the invention;

FIG. 10 shows a cross-sectional view of the hologram reticle shown inFIG. 9;

FIGS. 11A and 11B illustrate visual illustrations of light sources thatmay be used in a look-up table having a plurality of templates ofholographic fringes in accordance with an embodiment of the presentinvention;

FIG. 12 illustrates a top view of a hologram reticle in accordance withan embodiment of the invention;

FIG. 13 shows a cross-sectional view of the hologram reticle shown inFIG. 12;

FIG. 14A illustrates a top view of a hologram reticle in accordance withan embodiment of the invention;

FIG. 14B shows a more detailed view of a portion of the reticle shown inFIG. 14A;

FIG. 15 shows an embodiment of the invention, wherein a hologram reticleis directly illuminated to transfer or reconstruct the image to aphotoresist layer of a target;

FIG. 16 shows another embodiment of the present invention, wherein ahologram reticle is illuminated with an oblique beam to transfer theimage to a photoresist layer of a target;

FIG. 17 shows a reconstruction scheme in accordance with an embodimentof the invention, wherein a holographic representation of an image isduplicated on a top layer of photoresist on a target;

FIG. 18 illustrates the target of FIG. 17, wherein the top layer ofphotoresist having the holographic representation of an image isilluminated to reconstruct the image on a bottom layer of photoresistdisposed below the top layer of photoresist on the target;

FIG. 19 shows a hologram reticle in accordance with embodiments of thepresent invention having defects thereon;

FIG. 20 shows a semiconductor wafer having a material layer that hasbeen patterned using the hologram reticle of FIG. 19, wherein thehologram reticle defects are not transferred to the wafer pattern;

FIG. 21 illustrates a cross-sectional view of photoresist formed over aworkpiece, illustrating that the depth of focus may be varied to patternat a predetermined vertical depth within the photoresist in accordancewith an embodiment of the present invention;

FIG. 22 shows a prior art cross-sectional view of photoresist patternedcompletely in the vertical direction;

FIG. 23 shows an embodiment of the invention, wherein the depth of focusis varied at a plurality of locations, to create a 3-D pattern in thephotoresist layer;

FIGS. 24A through 24D illustrate cross-sectional views of a workpiece atseveral stages of manufacturing, wherein three-dimensional patterns areformed in a photoresist, and the patterns are filled with a material toform 3-D structures in a material layer;

FIG. 25 illustrates a cross-sectional view of a semiconductor wafer inaccordance with an embodiment of the invention, wherein multiple layersof interconnect are patterned within a single resist layer;

FIG. 26 show a prior art multi-layer device formed by a plurality ofsequential deposition steps and patterning steps of photoresist andinterconnect layers; and

FIGS. 27 and 28 illustrate examples of 3-D pattern formation within aphotoresist in accordance with an embodiment of the invention.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely, to a lithography reticle andmethod for patterning semiconductor wafers. Embodiments of the inventionmay also be applied, however, to other fields of lithography andlithography for other types of targets.

FIG. 4 is a flow chart 124 illustrating methods of manufacturing andusing a hologram reticle in accordance with embodiments of the presentinvention. First, the desired pattern layout is prepared (step 126). Thedesired pattern layout, also referred to herein as an image, preferablycomprises a pattern that will be transferred to a material layer of atarget or wafer 120/220/420 (see FIGS. 15, 18 and 23, respectively). Thepattern layout is converted into a holographic fringe pattern (step128), preferably using an encoding technique such as computer generatedholography (CGH), as an example. The encoding hologram imaging techniquemay utilize software adapted to implement a local encoding technique(LET) in one embodiment. Alternatively, the encoding hologram imagingtechnique may comprise a fast Fourier transform (FFT) method ofgenerating a holographic fringe pattern, as examples. A preferredembodiment of the programming code in C for the encoding of the patternlayout into a holographic fringe pattern is disclosed in Appendix A,which may be found in the file “TSM02-0658, Appendix A” of the computerprogramming listing appendix provided on compact disc submitted withthis patent application, which is incorporated by reference. However,the C code disclosed herein is exemplary, and the embodiments describedherein may be implemented in other types of code and form.

Referring again to the flow chart 124 of FIG. 4, next, in someembodiments of the invention, a hologram reticle 140/240/340/440 ismanufactured having the holographic fringe pattern patterned into anopaque layer (step 130). The hologram reticle 140/240/340/440 is thenused to pattern a first photoresist layer 122 on a target (step 133)(see FIGS. 15-16). Portions of the target first photoresist layer arethen removed (step 134), and then the target first photoresist layer 122is used as a reticle to pattern a material layer of the target (step135).

In another embodiment, the target comprises a first photoresist layerand a second photoresist layer formed over the first photoresist layer,as shown in FIGS. 17 and 18. The hologram reticle having a holographicfringe pattern is used to pattern the second photoresist layer (step132). The second photoresist layer of the target is then used to patternthe first photoresist layer of the target (step 136) with the image, andportions of the first photoresist layer of the target are removed (step137). The first photoresist layer is then used as a reticle to patternthe image onto a material layer of the target (step 138).

In yet another embodiment, no hologram reticle is required, and thetarget comprises a first photoresist layer and a second photoresistlayer formed over the first photoresist layer. The second photoresistlayer of the target is patterned directly with the holographic fringepattern (step 131). The target second photoresist layer is then used topattern the first photoresist layer of the target (step 136), andportions of the first photoresist layer are removed (step 137). Thefirst photoresist layer is then used as a reticle to pattern a materiallayer of the target (step 138).

Details of the preferred embodiments illustrated in the flow chart 124will be described further herein. Embodiments of the present inventionmay be used to pattern periodic (e.g., repeating) patterns, or generalpatterns having no particular repetition. After the hologram reticle ismanufactured, it may be stored, e.g., on a shelf, until it is time tomanufacture wafers with the image that is patterned in holographic formonto the hologram reticle. The hologram reticle may be used and storedin the same manner as traditional masks and reticles of the past.Advantageously, embodiments of the hologram reticles described hereinare compatible with existing exposure tools and lithography systemscurrently in use. The holograph reticles and methods of patterning usingholographic techniques described herein may be used to pattern aplurality of different types of material layers on a target, such asconductors, insulators and semiconductors, as examples.

FIG. 5 shows a top view of a hologram reticle 140 having a holographicfringe pattern 142 formed in an opaque layer 146 (see FIG. 6), inaccordance with an embodiment of the present invention. The originalpattern layout to be patterned on the target (such as the pattern ofopaque layer 14 shown in the prior art drawing of FIG. 1) and theencoded holographic fringe pattern 142, shown in FIG. 5, are quitedifferent, in accordance with embodiments of the invention. Theholographic fringe pattern 142 is preferably computer generated, and mayappear visually to the eye of a viewer as a plurality of random dots orapertures, as shown. The image to be patterned on the target isgenerally not visibly recognizable in the pattern 142 formed on thehologram reticle. However, the holographic fringe pattern correlates tothe desired pattern layout or image that will be transferred to thetarget 120 (see FIG. 20). The original image will appear after thereconstruction process on the target 120.

FIG. 6 illustrates a cross-sectional view of the hologram reticle 140shown in FIG. 5. The hologram reticle 140 includes a substrate 144 andan opaque material 146 disposed over the substrate 144. The substrate144 preferably comprises a transparent material, such as quartz, andalternatively may comprise other transparent materials, for example. Thesubstrate 144 preferably comprises a thickness of about 1 mm, for acommercially available diffraction optical element, to about one-quarterinch for a conventional 6 inches quartz mask, as examples.Alternatively, the substrate 144 may comprise other thicknesses.

The opaque material 146 preferably comprises a metal such as chrome, andmay alternatively comprise other metals and opaque materials, forexample. The opaque material 146 is preferably about 700 nm to 1000 nmthick, for example, although the opaque material 146 may alternativelycomprise other thicknesses. The opaque material 146 is preferablypatterned by depositing a photoresist over the opaque material 146,patterning the photoresist using an electron beam or laser, as examples,(although other patterning methods may be used) removing exposed (orunexposed) portions of the photoresist, and then using the photoresistas a mask to remove portions of the opaque material 146. Alternatively,rather than using a photoresist, the opaque material 146 may be directlypatterned by a reactive ion etch (RIE) process or by ion milling, asexamples. The hologram reticle 140 preferably comprises a transmissive,thin-film, binary hologram reticle, as shown in FIG. 6.

In another embodiment, shown in FIG. 7, the hologram reticle 240 maycomprise phase shifting regions 248 disposed proximate the substrate 244between portions of the opaque regions 246, in particular, disposed orformed over portions of the holographic fringe pattern 242. The phaseshifting regions 248 may comprise an additional layer of transparentmaterial, as shown, or alternatively, portions of the substrate 244 maybe removed to reduce the thickness of the substrate 244 and createphase-shifting regions, for example (not shown). The hologram reticlemay be implemented in any other reticle configuration, such as areflective volume, thin-film, binary, phase, or imprint with physicalcontact reticle, as examples.

FIG. 8 shows a cross sectional view of the hologram reticle 140 shown inFIG. 5. In one embodiment of the present invention, a Computer-GeneratedHolography encoding technique, such as an FFT encoding technique, isused to encode the entire image, the entire image being represented bythe letter “S” in FIGS. 5 and 8, into a pattern for a hologram reticle.FFT is a technology used in the fields of mathematics, physics, anddigital imaging processes, for example. With FFT, for each image S shownin FIGS. 5 and 8, holographic fringe must be calculated across theentire hologram.

In accordance with another embodiment of the present invention, an LETencoding technique is used to encode only a portion of the image into apattern for a hologram reticle. The portion of the image encoded to thehologram reticle is represented by the letter “S” in FIGS. 9 and 10,which illustrate a top view and a cross-sectional view, respectively, ofa hologram reticle 340 in accordance with an embodiment of theinvention. The portion of the image S of FIGS. 9 and 10 has a width mand a height n. Thus, in the LET encoding technique, the image isencoded into an m×n area on the hologram reticle 340. A plurality ofimage portions S are encoded using LET in accordance with an embodimentof the present invention, until the entire surface of the image isencoded into a holographic representation.

By using an LET, for each image portion S, only the area A which isdefined by m×n needs to be calculated. This is advantageous in that thecalculation time is greatly reduced. For example, a six inch reticle mayhave a total area of about 132,000 μm by 132,000 μm, and an LET area Amay be, for example, about 100 μm×100 μm. That is, approximately over0.5 million points of data may need to be calculated. The use of LET inaccordance with embodiments of the present invention advantageouslyreduces the time required for the calculation process to encode theimage into a holographic pattern, and reduces the use of computerresources required for the calculation process. Using an LET not onlysaves time but also makes the intensity, phase, and DOF of individualpoints in the patterning process more controllable.

A “look-up table” concept may be used to further reduce the timerequired for the large number of calculations required. The look-uptable may comprise a plurality of visual illustrations of light sourcesthat may be selected. For example, the visual illustrations of lightsources may comprise a fringe pattern from a 1×1 matrix single pointlight source such as the one shown in FIG. 11A, or a fringe pattern froma 3×3 matrix three point light source such as the one shown in FIG. 11B.Alternatively, the visual illustrations of light sources may compriseother numbers and arrangements of light source matrixes, such as 1×2,1×3, 1×4, . . . 2×1, 2×2, 2×3, 2×4 . . . 4×4, 4×1, 4×2, 4×3, 4×4, 4×5,etc., as examples, not shown. The look-up table may include a pluralityof templates of fringe patterns such as the ones shown in FIGS. 11A and11B, for example. The number of fringe patterns in the look-up tabledepends on the complexity of the layout, for example. The intensity ofthe individual image portion S of FIGS. 9 and 10 may be controlled byadjusting the size of the area A. The reconstruction characteristics ofthe image portion S can also be controlled by modifying the dimensions mand n.

The encoding of portions of the image is repeated until the entirereticle is encoded, as shown in FIGS. 12 and 13. Each portion encoded S1has an associated area m1×n1, and associated area m2×n2, for portion S2,for example. Note that if the area of m2×n2 is larger than the area ofm1×n1, then the intensity of S2 will be higher than the intensity of S1.However, the intensity of S1 and S2 can be controlled individually bycontrolling the size of the encoding area.

S1 and S2 denote two individual patterns or image portions, and can beconsidered as two points of light sources. The arrows represent thelight paths coming from the hologram reticle 340 and focusing to thetarget (to form image portion S) during the reconstruction process. Thearea m by n denotes how large the area or how many pixels contribute toreconstruct the image portion S during the imaging or reconstructionprocess. The unit of m and n may comprise length (for example, severalμm or nm) or simply pixels, and may alternatively comprise a minimumcomponent size on the reticle 340. The size or dimension of m and n maybe approximately between several to hundreds of μm in one embodiment.

The individual intensity will be decreased if there is overlapping ofthe encoded area. An illustration of this phenomena is shown in a topview of a hologram reticle 340 in FIG. 14A. The intensity decreasingcoefficient (IDC) may be expressed by Equation 1:

$\begin{matrix}{{\frac{1}{2} \times \frac{1}{mn} \times \left\{ \left\lbrack {A_{1} \otimes A_{2}} \right\rbrack \right\}};} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

where A₁

A₂ represents the area of overlapping, with A₁ being the amount ofhorizontal overlap and A₂ being the amount of vertical overlap, whereinm1=m2=m and n1=n2=n. FIG. 14B shows a more detailed view of the area ofoverlap.

Equation 1 expresses the IDC for two overlapping image portions S1 andS2. Similarly, the IDC for three overlapping image portions may berepresented by Equation 2:

$\begin{matrix}{{\frac{1}{2} \times \frac{1}{mn} \times \left\{ {\left\lbrack {A_{1} \otimes A_{2}} \right\rbrack + \left\lbrack {A_{1} \otimes A_{3}} \right\rbrack} \right\}} - {\frac{1}{3} \times \frac{1}{mn} \times \left\{ \left\lbrack {A_{1} \otimes A_{2} \otimes A_{3}} \right\rbrack \right\}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

and the IDC for four overlapping image portions may be represented byEquation 3:

$\begin{matrix}{{\frac{1}{2} \times \frac{1}{mn} \times \left\{ {\left\lbrack {A_{1} \otimes A_{2}} \right\rbrack + \left\lfloor {A_{1} \otimes A_{3}} \right\rfloor + \left\lfloor {A_{1} \otimes A_{4}} \right\rfloor} \right\}} - {\frac{1}{3} \times \frac{1}{mn} \times \left\{ {\left\lfloor {A_{1} \otimes A_{2} \otimes A_{3}} \right\rfloor + \left\lfloor {A_{1} \otimes A_{2} \otimes A_{4}} \right\rfloor + \left\lfloor {A_{1} \otimes A_{3} \otimes A_{4}} \right\rfloor} \right\}} + {\frac{1}{4} \times \frac{1}{mn} \times \left\{ \left\lfloor {A_{1} \otimes A_{2} \otimes A_{3} \otimes A_{4}} \right\rfloor \right\}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

If two reconstruction image portions S1 and S2 are located too closetogether, their A1 and A2 will overlap on the hologram reticle, as shownin FIG. 14B. The size of A will affect the intensity of S; therefore,when there is overlap, the intensity of image portions S1 and S2 areboth decreased because by sharing the overlapping area [A1

A2] with each other, the “effective” areas of A1 and A2 are decreased.In this case, the IDC quantifies the effect of the decrease area. TheIDC depends on the location and distance of the overlapping. Accordingto the IDC, the loss of intensity can be compensated by increasing thesize of the area A.

FIG. 15 illustrates an embodiment of the invention, wherein a hologramreticle 140 is directly illuminated with illumination or a beam fromenergy source 154 to transfer or reconstruct the image to a target 120.The target 120, shown in cross-sectional view, may comprise asemiconductor wafer, as an example, including a workpiece 121, amaterial layer 155 disposed over the workpiece, and a layer ofphotoresist 122 disposed over the material layer 155. The workpiece 121may include a semiconductor substrate comprising silicon or othersemiconductor materials covered by an insulating layer, for example. Theworkpiece 121 may also include other active components or circuits, notshown. The workpiece 121 may comprise silicon oxide over single-crystalsilicon, for example. The workpiece 121 may include other conductivelayers or other semiconductor elements, e.g. transistors, diodes, etc.Compound semiconductors, GaAs, InP, Si/Ge, or SiC, as examples, may beused in place of silicon. The material layer 155 may comprise aconductive material, insulative material, semiconductive material, orother materials, as examples. The photoresist 122 comprises an organicor polymer resist typically used in lithographic techniques.

In this reconstruction method, the target or wafer 120 is directlyilluminated, with a hologram reticle 140 (or 240 or 340) describedherein being disposed between the source of illumination (e.g., energysource 154) and the target 120. The energy source 154 may comprise acoherent or partial coherent light source such as a laser source, asexamples, although other energy sources may alternatively be used. Inthis embodiment of the invention, energy is directed substantiallyperpendicular to the surface of the target 120. The energy may comprisea beam, such as an electron beam or an ion beam, as examples. Theholographic fringe pattern of the hologram reticle 140 is adapted toexpose the photoresist 122 and form the desired image on the photoresist122 of the target 120. The photoresist 122 is then developed, andportions of the photoresist 122 are removed. The photoresist is thenused as a mask to etch the material layer 155 of the target 120 and formthe image within the material layer 155.

The reconstruction processes for the hologram imaging techniquedescribed herein preferably comprise a combination of constructive anddestructive interference. The incident angle of illumination alsoaffects the hologram imaging technique reconstruction.

In another embodiment, shown in FIG. 16, a hologram reticle 140 isilluminated with an oblique beam (e.g., a beam that is directednon-perpendicular to the surface of the workpiece 121) to transfer theimage to the target 120. The oblique beam is used to illuminate thetarget 120 through the hologram reticle 140. In this embodiment, a waferblade 150 may be disposed between the target 120 and the hologramreticle 140, and/or a reticle blade 152 may be disposed between theenergy source 154 and hologram reticle 140. The wafer blade 150 and/orreticle blade 152 may be moved while the target 120 is illuminated, inthe same or opposing directions, for example. The incident illuminationlight or oblique beam is directed at an angle to project a shadow on thewafer blade 150. The reticle blade 152 controls the size of the slit, tooptimize the performance of the hologram reticle 140 lithography system.The reticle blade 152 is adapted to block the unwanted incidentillumination. Similarly, the wafer blade 150 is adapted to blockunwanted diffraction lights, such as high order diffraction beams, as anexample. The angle θ may comprise 30 degrees, as an example, and morepreferably, angle θ ranges from 15 to 45 degrees, for example.

Embodiments of the invention may also be implemented on a target havingmultiple layers of photoresist, also referred to herein as top surfaceimaging (TSI), as shown in FIGS. 17 and 18. TSI involves patterningfeatures on a target using two photoresist layers 257 and 256 depositedover the target 220, with a spacer 258 separating the two photoresistlayers 257 and 256. The top photoresist layer 257 preferably comprises athickness of about 500 Å, and the bottom photoresist layer 256preferably comprises a thickness of about 3000 Å, as examples, althoughthe top and bottom photoresist layer 257 and 256 may alternativelycomprise other thicknesses. The top photoresist 257 is used to patternthe underlying photoresist layer 256. The spacer 258 or buffer layerpreferably comprises a transparent material that is adapted to separatethe top photoresist 257 from the bottom photoresist layer 256 (oftenreferred to as a “button” layer) by a predetermined distance; e.g., thespacer may comprise a thickness between about 3,000 to 10,000 Å, asexamples. The spacer 258 may comprise spin-on glass (SOG) orborophosphosilicate glass (BPSG), as examples, although alternatively,other optically transparent materials may be used. In this embodiment,the top photoresist 257 functions as a secondary hologram reticle,implemented in TSI on the target 220. The secondary hologram reticle 257is also defect-withstanding and CD-error insensitive, as is the hologramreticle 240, to be described further herein.

FIG. 17 shows a reconstruction scheme in accordance with an embodimentof the invention, wherein the holographic representation of the hologramreticle is duplicated on the top layer of photoresist 257 on a target220. Using an exposure tool 260, energy from an energy source 254 ispassed through a hologram reticle 240 to pattern the top photoresistlayer 257 with the holographic representation of an image. The exposuretool 260 may comprise, as examples, an optical exposure tool such as astepper, scanner or imprint tool, although other exposure tools mayalternatively be used. The target top photoresist layer 257 is thendeveloped, preferably using a gas or dry development, as examples,without destroying the bottom layer of photoresist 256. Preferably,during the exposure step and subsequent development step of the topphotoresist layer 257, the remaining layers of the target 220, such asworkpiece 221, material layer to be patterned 255, photoresist layer256, and spacer 258, remain substantially unaffected.

In one embodiment, the TSI latent pattern having the holographic fringerepresentation of the desired image to be patterned may be formed in thetop photoresist layer 257 by a lithography process with a hologramreticle as shown in FIG. 17, or alternatively, the TSI latent pattern beformed by direct-writing a holographic representation of the desiredimage onto the top photoresist layer 257 (not shown). Alternatively, theholographic representation of the desired image may be formed into thetop photoresist layer 257 by another maskless lithography process suchas by RIE or by ion milling, as examples (also not shown).

FIG. 18 illustrates the target 220 of FIG. 17, wherein a reconstructedimage is formed on the bottom photoresist layer 256 that issubstantially the same as the original image. The patterned top layer ofphotoresist 257 is illuminated with a beam of energy from the energysource 254 to reconstruct the desired image on the bottom layer ofphotoresist 256. The photoresist 257 that is patterned with aholographic representation of the desired image is removed, and thespacer 258 is removed. The bottom layer of photoresist 256 is developed,and then the bottom photoresist layer 256 is used as a mask to patternthe material layer 255 of the target 220. The material layer 255 thencomprises the desired image. The bottom photoresist layer 256 is thenremoved, and subsequent processing steps may then be performed on thetarget 220 to complete the manufacturing process.

FIG. 19 shows a top view of a hologram reticle 140 in accordance withembodiments of the invention having defects 118 disposed thereon. Due tothe nature of a holographic pattern, any defects 118 on the hologramreticle 140 will not be transferred to a target such as thesemiconductor wafer 120 shown in FIG. 20 when the hologram reticle 140is used to pattern the wafer 120. The holographic representation of theimage breaks the one-to-one relationship between the reticle pattern andthe image in the material layer 155 patterned. Advantageously, anydefects 118 on the hologram reticle 140 merely affect the intensity ofthe holographic image, and are not transferred to the desired image thatis patterned within the material layer 155 of the wafer 120.

FIG. 21 illustrates a cross-sectional view of photoresist 322, showinghow the depth of focus (DOF) may be varied to pattern at a particularvertical depth within the photoresist 322 perpendicular to the target320 surface, in accordance with an embodiment of the present invention.The target or wafer 320 comprises a workpiece 321 and a material layer355 to be patterned. A layer of photoresist 322 has been formed over thematerial layer 355. The depth of focus, using the hologram reticle 340,may be varied to pattern at any depth within the photoresist 322, asshown.

In one embodiment of the present invention, a two-photon process is usedto pattern a photoresist layer. A two-photon process is a non-linearquantum photochemical reaction. With suitable situation and material, amolecule can absorb two low energy photons (for example, having awavelength of about 800 nm) rather than one high energy photon (having awavelength of about 400 nm). This non-linear phenomenon happens only inan area with a very high density of photons. In accordance withembodiments of the present invention, a very high density area iscreated by virtual light sources of the holographic reconstructionimages. More specifically, a 3-D structure pattern may be created orreconstructed in a photoresist layer using a holographic reticle with alaser beam.

With sufficient illumination intensity, the resist 322 will be exposedby absorbing two low energy photons such as infrared (IR) photons ratherthan one high energy photon such as the ultraviolet (UV) photon. Thistwo-photon process occurs close to the focal point 366 with high photondensity. In this manner, one spot (e.g., focal point 366) may be exposedat a time using a two-photon process. In contrast, prior artphotolithography techniques involve using an traditional imaging systemwith a conventional mask 10 to pattern resist 22 on a target 20completely in the vertical direction, as shown in FIG. 22. The condensedenergy beam induces the vertical cylinder shape of resist 22 that isexposed, in prior art photolithography techniques.

In accordance with an embodiment of the present invention, a target 420comprises a workpiece 421 and a material layer 455 deposited over theworkpiece 421, as shown in FIG. 23. A photoresist layer 422 is depositedover the material layer 455. The photoresist 422 may be patterned at twoor more depths, or a range of depths, as shown in FIG. 23, to create a3-D pattern, e.g., using a two-photon illumination process. A directwrite scheme may be used to construct 3-D structures in the photoresistlayer 422, for example. By using the holographic imaging processesdescribed herein, a plurality of locations within the layer ofphotoresist 422 may be exposed in a single exposure.

For example, generally, a semiconductor manufacturing process contains afront-end and back-end, referring to periods of time in themanufacturing flow. The frond-end is the portion of the manufacturingprocess in which silicon and polysilicon processes occur, such asdeposition, doping and implanting processes, to create active devicessuch as transistors and other circuit elements. The back-end is theportion of the manufacturing process after the front-end, in which themetallization layers, contact hole layers and other connecting layersfor the front-end devices are formed. For a typical foundry chip, thereare about two silicon-type layers formed in a front-end, and about eightcontact hole layers and eight metallization layers formed in a back-end:a total of 18 layers, for example. It is notable that 16 of these 18layers are processed only for connecting purposes. Because traditionallithography can only form an image on a two-dimensional plane across awafer surface, these 16 connection layers have to be processed one byone, requiring a different mask for each layer. By using a holographicreticle combined with a two-photon process as described herein,three-dimensional images can be reconstructed in a photoresist layer,thus patterning more than one layer in a single exposure.

FIGS. 24A through 24D show cross-sectional views of a semiconductordevice 520 in which a holographic reticle and two-photon process areused to pattern a 3D image of a semiconductor device 520, saving onelevel of lithography patterning. A workpiece 512 is provided, and aphotoresist layer 570 is deposited over the workpiece 512. Thephotoresist 570 in this embodiment is preferably relatively thick,comprising a thickness of two or more material layers, for example. Thephotoresist 570 is patterned using a holographic reticle 440 such as theone shown in FIG. 23, and a two-photon process is used to illuminate thephotoresist 570 through the holographic reticle 440, for example. Thepattern 572 formed in the photoresist 570 in this embodiment comprises adual damascene pattern, including a contact pattern (the thin regions)and conductive line pattern (the thicker regions disposed over the thinregions). Patterned portions of the photoresist 570 are removed, asshown in FIG. 24B, and a material 574 such as a conductive material(although other materials may also be used) is deposited over thepatterned photoresist 570, as shown in FIG. 24C. Excess material 574 maybe removed from over a top surface of the photoresist 570, using achemical-mechanical polishing (CMP) process or other methods. Thephotoresist 570 is then removed, leaving a three-dimensional structureformed from the material 574, as shown in FIG. 24D. This isadvantageous, because prior art damascene patterning methods for metallayers require two separate mask levels. Thus, embodiments of thepresent invention reduce the number of patterning steps and reduce thenumber of masks required for semiconductor fabrication.

FIG. 25 illustrates an embodiment of the invention, wherein multiplelayers of interconnect are patterned within a single resist layerdisposed over a workpiece 421. Active areas 462 may be formed over theworkpiece 421, as shown, for example. In this example, seventeen or morelayers of metallization (M1-M9) and contact or via levels (V1-V8) may bereplaced by a single holographic imaging process, combined with a twophoton process. In comparison, FIG. 26 shows a prior art semiconductordevice 20 having a multi-layer interconnect, formed by sequentialdepositions and patterning of photoresist and interconnect layers. Thus,in accordance with embodiments of the present invention, many sequentialpatterning steps and lithography masks may be eliminated, savingprocessing time and expense of designing and making the masks.

FIGS. 27 and 28 illustrate examples of 3-D pattern formation within aphotoresist in accordance with an embodiment of the invention. In FIG.27, a 3-D image 464 which may comprise a pyramid, for example, isconverted into a holographic representation of the image, using an LETin one embodiment, although other methods may be used. The holographicrepresentation is patterned onto a mask 440, and the mask 440 is used topattern a single relatively thick layer of photoresist 470. Top, middleand bottom views of the photoresist 470 are shown. A material layer isdeposited over the photoresist 470 to fill the 3-D pattern, and thephotoresist is removed, leaving a 3-D structure formed over a workpiece(not shown in FIG. 27). Similarly, FIG. 28 illustrates a 3-D image 464comprising the letters A and Z that are transferred to a holographicpattern (not shown), and the three-dimensional image of the letters isreconstructed using a hologram reticle and two-photon process into aphotoresist layer 470 of a target, thus illustrating the capability offorming two layers of an image in one exposure, in accordance withembodiments of the present invention.

A short DOF and small focal point are required to induce exposed spotswith the two photon process described herein. The hologram reticles140/240/340/440 described herein produce a short DOF because of thecharacteristics of the holographic representation of the image. Highorder diffraction beams have a larger incident angle. The larger anglerepresents a higher numerical aperture (NA) and produce a shorter depthof focus (DOF). In accordance with embodiments of the present invention,a holographic pattern can be modified or designed so that it containsmore or less higher order fringes in order to control the individualDOF.

Embodiments of the present invention are useful and have application instatic holographic reticles, as described herein, wherein theholographic representation of the image is fixedly patterned into areticle. However, embodiments of the present invention also haveapplication in dynamic reticles, wherein the holographic fringerepresentation of the image may be altered or erased after beingpatterned into the reticle. Masks or reticles in which a dynamicholographic representation of an image may be patterned includeelectric-optical modulation devices such as a liquid crystal display(LCD), or micro-machined devices such as a special light modulator(SLM), as examples.

The holographic reticles described herein may comprise binary reticles,phase-shifted reticles, and/or volume reticles, for example. Fringes ona phase holographic reticle represent phase information rather thanintensity information, for example. A volume holographic reticlecomprises a holographic fringe representation of a 3-D structure, forexample.

Embodiments of the present invention achieve technical advantages as anovel hologram reticle and lithography process that isdefect-withstanding. Defects on the hologram reticle 140/240/340/440 arenot transferred to the image produced on a target. Due to thecharacteristics of the holographic representation of the image, defectsthat are not too large in size or number may be left remaining on thehologram reticle 140/240/340/440, yet defect-free targets may beproduced using the hologram reticle 140/240/340/440. This isadvantageous because defect repair may be reduced or eliminated,resulting in a cost savings and increased yield for manufacturedhologram reticles 140/240/340/440. If repair is needed, the hologramreticle 140/240/340/440 described herein is more durable for the repairprocess. Any defects on the hologram reticle 140/240/340/440 do notdirectly induce a flaw on a target, but rather, the defect influence isspread into the entire image, affecting intensity or contrast, or both,only slightly.

The multi-layer 3-D imaging technique using a holographic reticledescribed herein may be used with existing lithography tools,advantageously. No special design schemes or tools are required for theholographic reticle and patterning methods described herein.

Another advantage is that the hologram reticle 140/240/340/440 is CDerror insensitive: critical dimension (CD) errors on holographic reticlewill not affect the final image on the wafer or other targetsubstantially. For a diffraction element, pitch is more important thanthe CD.

A further advantage is the ability to precisely control and decrease theDOF and form 3-D structures in the photoresist layer on the target usinga two photon process. Combining the holographic reticle with a twophoton process produces an extremely short DOF, allowingthree-dimensional reconstruction in thick photoresist layers.Alternatively, the DOF may be increased to extend the lithographyprocess window, which is particularly advantageous on a topographicsubstrate.

Furthermore, an LET can be used to reduce the calculation time requiredto convert the image to be patterned to a holographic representation onthe hologram reticle 140/240/340/440. An LET can also be used to controlthe intensity of the individual image. A look-up table of fringes may beused to further reduce the time required for the conversioncalculations.

Additional advantages include compatibility with existing exposure toolsand lithography systems, and the ability to implement the hologramreticle 140/240/340/440 with TSI. Furthermore, the CGH algorithm used toconvert the image to a holographic representation of the image may bemodified to improve the image quality, including contrast, cornerrounding, and depth of focus, as examples.

The defect-withstanding hologram reticle 140/240/340/440 describedherein is particularly advantageous for use with X-ray Lithography(XRL), SCattering with Angular Limitation in Projection Electron beamLithography (SCALPEL), Extreme Ultra-Violet Reflective ProjectionLithography (EUVL), Ion-beam Projection Lithography (IPL), and E-beamLithography processes, as examples

Although embodiments of the present invention and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, while the hologram reticle 140/240/340/440 is describedherein as a transmissive reticle, (e.g. light is passed through thereticle towards the target), the hologram reticle 140/240/340/440 mayalternatively comprise a reflective reticle. As another example, it willbe readily understood by those skilled in the art that the selection ofthe target to be patterned using the hologram reticle described hereinmay be varied while remaining within the scope of the present invention.As examples, the target may comprise a semiconductor wafer, or mayalternatively comprise an optical device, or an organic material, asexamples. Embodiments of the present invention include targets such assemiconductor devices that have been patterned using the holographicreticles and methods of patterning described herein.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. A lithography reticle, comprising: a material having a pattern, thepattern including opaque regions and transparent regions, the patterncomprising a holographic representation of an image, wherein theholographic representation of the image is formed using aComputer-Generated Holography encoding technique.
 2. The lithographyreticle according to claim 1, wherein the material comprises: atransparent substrate; and an opaque material disposed over thesubstrate, wherein the pattern is formed in the opaque material.
 3. Thereticle according to claim 1, wherein the holographic representation ofan image comprises a holographic fringe pattern.
 4. The reticleaccording to claim 3, wherein the holographic fringe pattern comprises aplurality of small apertures, wherein the apertures do not visuallyresemble the image in a one-to-one relationship.
 5. The reticleaccording to claim 1, further comprising a phase-shifting materialdisposed over portions of the material.
 6. The reticle according toclaim 1, wherein the reticle is transmissive or reflective.
 7. Thereticle according to claim 1, wherein the material comprises a liquidcrystal display or a special light modulator.
 8. A method ofmanufacturing a lithography reticle, comprising: providing an image;creating a holographic representation of the image using a localencoding technique (LET); providing a material; and patterning thematerial with the holographic representation of the image, wherein thepatterned material comprises transparent regions and opaque regions. 9.The method according to claim 8, wherein patterning the opaque materialwith the holographic fringe pattern comprises patterning the opaquematerial with a plurality of small apertures, wherein the apertures donot visually resemble the image in a one-to-one relationship.
 10. Themethod according to claim 8, wherein providing the material comprisesproviding a substrate and disposing an opaque material over thesubstrate, wherein patterning the material comprises patterning theopaque material.
 11. The method according to claim 10, furthercomprising forming at least one phase-shifting region over a portion ofthe substrate.
 12. The method according to claim 8, further comprisingproviding a look-up table, the look-up table including a plurality offringe patterns for light sources, wherein creating the holographicrepresentation of the image comprises referring to the look-up table.13. The method according to claim 8, wherein creating the holographicrepresentation of the image comprises partitioning the image to aplurality of areas, and creating a holographic representation of eacharea.
 14. The method according to claim 8, wherein providing thematerial comprises providing a liquid crystal display or a special lightmodulator